It can be a hassle when your phone's battery runs out of juice and you have to hunt down a power outlet to recharge, but a flat battery is an even bigger hassle in implanted electronic medical devices, such as pacemakers. It often means invasive surgery to replace the battery or the entire unit, but now a new study has found that the use of solar cells implanted under the skin to power medical implants is a feasible approach.

The potential advantages of powering medical implants using solar energy to avoid the problems of replacing or recharging batteries has seen various research groups develop small solar cell prototypes that could be implanted under the skin and harness the energy of the light that penetrates the skin's surface to keep medical implants powered up.

To examine the feasibility of such technology, a team led by Lukas Bereuter of Bern University Hospital and the University of Bern in Switzerland developed 10 solar measurement devices that could be worn on the arm. The devices featured solar cells measuring 3.6 cm2 (0.5 in2) in size, which is small enough for implantation, and were able to measure the output power the cells generated. Optical filters also covered the cells to simulate the properties of the skin and its effect on the incoming light.

A total of 32 volunteers in Switzerland wore the devices for a week each during all four seasons of the year. The researchers found that regardless of the time of year, even the individual that returned the lowest power output was still able to generate 12 microwatts of electricity on average, which is more than the five to 10 microwatts required by a typical pacemaker.

"The overall mean power obtained is enough to completely power for example a pacemaker or at least extend the lifespan of any other active implant," says Bereuter. "By using energy-harvesting devices such as solar cells to power an implant, device replacements may be avoided and the device size may be reduced dramatically."

In addition to pacemakers, Bereuter thinks the technology could be scaled up for other solar-powered applications on people, with the total surface area of the solar cell, its placement and efficiency and the thickness of a patient's skin all aspects that would need to be taken into account.